Technical Abstract: A field study was conducted to use mid-day canopy to air temperature difference (delta T) to manage postharvest deficit irrigation of peach trees in San Joaquin Valley of California and its performance was evaluated. Delta T thresholds were selected, based on previous years’ stem water potential and delta T measurements, for four irrigation treatments: furrow and subsurface drip irrigation with or without postharvest water stress. In both growing seasons (2009-2010 and 2010-2011), the measured delta T values showed differences among treatments. An acceptable correlation was obtained when delta T was related to stem water potential (R2=0.47-0.65). The results also indicated that stem water potential in irrigation treatments with or without water stress should be maintained above -2 MPa or between -0.58 to -0.9 MPa, respectively. Deficit irrigation showed the differences in the total number of fruit and fruit weight per tree but not in weight per fruit. The relationship between weight per fruit and postharvest irrigation amount for last four year study shows that up to 60 % water saving can be achieved with minimal impact on fruit size.